Annulus Seal Utilizing Energized Discrete Soft Interfacial Sealing Elements

ABSTRACT

A seal assembly for sealing an annulus between inner and outer wellhead members comprises an energizer ring having inner and outer legs separated by a slot, formed of a high strength elastic material and having a central axis and an inner diameter seal ring formed of an inelastic material located on an inner side of the inner leg for creating a seal between the inner wellhead member the energizer. An outer diameter seal ring formed of an inelastic material is located on an outer side of the outer leg for creating a seal between the energizer and the outer wellhead member. The seal assembly may have an initial radial dimension from inner surface of the inner diameter seal ring to an outer surface of the outer diameter seal ring that is adapted to be greater than a radial width of the annulus, causing the legs to deflect towards each other when inserted in the annulus.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates in general to wellhead assemblies and inparticular to seal assemblies for sealing between inner and outerwellhead members.

2. Description of the Related Art

Seals are used between inner and outer wellhead tubular members tocontain internal well pressure. The inner wellhead member may be acasing hanger that supports a string of casing extending into the wellfor the flow of production fluid. The casing hanger lands in an outerwellhead member, which may be a wellhead housing, a Christmas tree, or acasing head. A packoff (or other seal assembly) seals the annulusbetween the casing hanger and the outer wellhead member. Alternately,the inner wellhead member can be a tubing hanger located in a wellheadhousing and secured to a string of tubing extending into the well. Apack off (or other seal assembly) seals the annulus between the tubinghanger and the wellhead housing. In another alternative design, theinner wellhead member may be an isolation sleeve, such as might be usedto isolate high pressure, abrasive fracturing fluids from certainportions of the wellhead. A packoff (or other seal assembly) seals theannulus between the isolation sleeve and the outer wellhead member.

A variety of annulus seals of this nature have been employed.Conventional annulus seals include, for example, elastomeric andpartially metal and elastomeric rings. Prior art subsea stab type sealsmay utilize elastomeric materials which are compressed into aninterference fit annulus. These are simple designs, easy to install,retain a reasonable constant load when unpressurised over time due totheir inherent elasticity and are soft enough to flow and seal on minordefects. However such materials have a limited range of use in terms oftemperature and fluid compatibility. They may swell and degrademechanically in certain fluid environments, such as those found in manywellheads, and can suffer from explosive failure if subjected to rapidlydecreasing pressure in a gas environment.

Prior art seal rings made entirely of metal for forming metal-to-metalseals are also employed. In order to cope with internal stressing remotefrom the interfaces, metal seals of the prior art are made from hardhigh strength materials which make sealing at the interface difficultand require generating of huge loads to provide any degree of damagetolerance. This in turn will itself cause damage to the same surfaces.To overcome this, coatings in the form of spray coatings or plating ormelted inlays, such as brazing have been used to bond a secondary softermaterial to the metal seal. These coatings are often difficult to apply,costly, inefficient in material usage, tend to increase the hardness ofthe sprayed material and are typically difficult to apply thick enoughto provide the volume of material required to seal on serious defects.

A third option for the prior art has been to use inelastic thermoplasticmaterials such as polytetrafluoroethylene, or moulded graphite for thesealing apparatus. These do not have any inherent elasticity and sorequire some secondary parts, such as internal springs, to provide anelastic response to the changing environment that ensures the sealretains a reasonable constant load when unpressurised over time and soensuring a seal is maintained at all times. Due to the low strength ofthermoplastic materials they generally cannot sustain the loads requiredto cause significant plastic flow at the interface and so do not tend toseal well on damaged surfaces.

Therefore while metal or inelastic materials allow a much widertemperature range, do not swell or degrade mechanically in most fluidenvironments and do not suffer from explosive gas decompression, they dorepresent many other technical problems, most notably an inability toseal on damaged surfaces. Damage to subsea parts cannot be fullymonitored or controlled and therefore seal failure due to damagedsurfaces represents a significant cost risk when running equipmentsubsea.

Therefore, there is a need for an annulus seal that would maintain aseal that can seal on serious surface defects, operate over a much widertemperature range, does not swell or degrade mechanically in most fluidenvironments, does not suffer from explosive gas decompression and canbe easily and cheaply manufactured.

SUMMARY OF THE INVENTION

In view of the foregoing, various embodiments of the present inventionadvantageously provide seal assemblies to address shortfalls of theprior art. Various embodiments of the present application use softinelastic materials in a situation where the seal is highly loaded, byremoving the inelastic material from the highly stressed unsupportedareas and replacing it with a high strength energizer. Alternativeembodiments use thick soft metallic materials, in fully annealedcondition if required, with no need for a metallurgical or other type ofbond to the base component.

More specifically, the current application provides a seal assembly forsealing an annulus between inner and outer wellhead members comprisingan energizer ring having inner and outer legs separated by a slot whichis formed of a high strength elastic material and has a central axis, aninner diameter seal ring formed of an inelastic material located on aninner side of the inner leg for creating a seal between the innerwellhead member and the energizer, and an outer diameter seal ringformed of an inelastic material located on an outer side of the outerleg for creating a seal between the energizer and the outer wellheadmember.

In certain embodiments, the seal assembly has an initial radialdimension from inner surface of the inner diameter seal ring to an outersurface of the outer diameter seal ring that is adapted to be greaterthan a radial width of the annulus, causing the legs to deflect towardseach other when inserted in the annulus. This deflection generatesradial loads in the energizer which in turn creates contact loads inboth seal rings.

The seal assembly may further comprise a plurality of anti-extrusiondevices for restricting an axial dimension of each of the seal ringswhen the seal assembly is set. The anti-extrusion devices may comprisean annular band on the inner side of the inner leg and protruding inwardfrom the inner leg, an annular band on the outer side of the outer legand protruding outward from the outer leg, and an annular recess in eachof the bands. Each of the seal rings is located in one of the recessesand radially protrudes therefrom prior to setting of the seal assembly.Prior to setting of the seal assembly, an axial dimension of eachannular recess is greater than an axial dimension of each seal ring. Theannular bands are adapted to contact the inner and outer wellheadmembers when the seal ring assembly is set.

In an alternative embodiment, the anti-extrusion devices comprise a pairof wedge rings, the wedge rings having a mating wedge surface thatcauses one of the wedge rings to slide radially inward and the other toslide radially outward. In another alternative embodiment, theanti-extrusion device comprises an inner wedge ring having an innerwedge ring surface, an outer wedge ring having an outer wedge ringsurface, and inner and outer wedge surfaces on a base of the energizerthat slidingly engage the inner wedge ring surface and the outer wedgering surface during setting of the seal assembly to convey the wedgerings apart from each other.

In certain other embodiments, the seal assembly further comprises asecond energizer ring having inner and outer legs facing in an oppositedirection to said first mentioned energizer ring. The inner diameterseal ring and the outer diameter seal ring may be formed of an inelasticmaterial selected from a group consisting of lead, tin, silver, gold,tantalum, virgin polytetrafluoroethylene, filled polytetrafluoroethyleneor polyetheretherketone, or compression molded graphite.

In other embodiments, the current application also provides a wellheadassembly comprising an outer wellhead member having a bore and an axis,an inner wellhead member located in the bore and defining an annulusbetween the inner and outer wellhead members, an energizer ring havinginner and outer legs separated by a slot, formed of a high strengthelastic (nominally metallic) material and having a central axis, aninner diameter seal ring formed of an inelastic material located on aninner side of the inner leg for creating a seal between the innerwellhead member and the energizer, and an outer diameter seal ringformed of an inelastic material located on an outer side of the outerleg for creating a seal between the energizer and the outer wellheadmember, wherein the legs deflect towards each other when inserted in theannulus, causing the seal rings to radially deform.

The wellhead assembly may further comprise a plurality of anti-extrusiondevices for restricting an axial dimension of each of the seal ringswhen set in the annulus. The anti-extrusion devices may comprise anannular band on the inner side of the inner leg and protruding inwardfrom the inner leg, an annular band on the outer side of the outer legand protruding outward from the outer leg, and an annular recess in eachof the bands, wherein prior to setting of the seal assembly each of theseal rings is located in one of the recesses and radially protrudestherefrom and an axial dimension of each annular recess is greater thanan axial dimension of each seal ring.

Other embodiments of the current application provide an apparatus forsealing an annulus between inner and outer wellhead members, the sealassembly comprising a first energizer ring having inner and outer legsseparated by a slot, formed of a high strength elastic (nominallymetallic) material and having a central axis, a second energizer ringhaving inner and outer legs facing in an opposite direction to the firstenergizer ring, an inner diameter seal ring formed of an inelasticmaterial located on an inner side of each of the inner legs for creatinga seal between the inner wellhead member the energizers, an outerdiameter seal ring formed of an inelastic material located on an outerside of each of the outer legs for creating a seal between theenergizers and the outer wellhead member, and a plurality ofanti-extrusion devices for restricting an axial dimension of each of theseal rings when the seal assembly is set.

In one embodiment of such apparatus, when a force is applied in an axialdirection to set the apparatus in the annulus, the inner seal rings moveinward to abut the inner wellhead member and the outer seal rings moveoutward to abut the outer wellhead member. The anti extrusion devicesmay comprise an inner wedge ring having an inner wedge ring surface, anouter wedge ring having an outer wedge ring surface, and inner and outerwedge surfaces on a base of each energizer that slidingly engage theinner wedge ring surface and the outer wedge ring surface during settingof the apparatus to convey the wedge rings apart from each other.

Yet another embodiment of the present application provides a method forsealing an annulus between inner and outer wellhead members, the methodcomprising the steps of: (a) positioning an energizer within theannulus, the energizer ring having inner and outer legs separated by aslot, formed of a high strength elastic (nominally metallic) materialand having a central axis; (b) creating a seal between the innerwellhead member and the energizer with an inner diameter seal ringformed of an inelastic material located on an inner side of the innerleg; and (c) creating a seal between the energizer and the outerwellhead member with an outer diameter seal ring formed of an inelasticmaterial located on an outer side of the outer leg.

Steps (b) and (c) may further comprise applying sufficient force to theenergizer to deflect the legs of the energizer towards each other byelastic deformation and cause plastic deformation of the inner diameterseal ring and outer diameter seal ring. Steps (b) and (c) may be furtheraided by the application of fluid pressure which expands the energizer,causing the legs of the energizer to deflect away from each other,thereby causing further plastic deformation of the inner diameter sealring and outer diameter seal ring. The method may also further comprisethe step of limiting the axial expansion of the inner diameter seal ringand the outer diameter seal ring with an anti-extrusion device. The stepof limiting the axial expansion of the inner diameter seal ring and theouter diameter seal ring may be performed by an annular band on theinner side of the inner leg and protruding inward from the inner leg andan annular band on the outer side of the outer leg and protrudingoutward from the outer leg, wherein an annular recess is formed in eachof the bands and wherein prior to setting of the seal assembly, each ofthe seal rings is located in one of the recesses and radially protrudestherefrom, and an axial dimension of each annular recess is greater thanan axial dimension of each seal ring.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the features and advantages of theinvention, as well as others which will become apparent, may beunderstood in more detail, a more particular description of theinvention briefly summarized above may be had by reference to theembodiments thereof which are illustrated in the appended drawings,which form a part of this specification. It is to be noted, however,that the drawings illustrate only various embodiments of the inventionand are therefore not to be considered limiting of the invention's scopeas it may include other effective embodiments as well.

FIG. 1 is a sectional view of portions of a wellhead assembly providinga annulus seal;

FIG. 2 is a sectional view of a portion of a seal assembly according toan embodiment of the present invention;

FIG. 3 is a sectional view of the seal assembly of FIG. 2;

FIG. 4 is a sectional view of a portion of a seal assembly according toan alternative embodiment of the present invention; and

FIG. 5 is a sectional view of the seal assembly of FIG. 4.

FIG. 6 is an additional sectional view of the seal assembly of FIG. 4.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, which illustrate embodiments ofthe invention. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theillustrated embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.Like numbers refer to like elements throughout. Prime notation, if used,indicates similar elements in alternative embodiments.

FIG. 1 illustrates, for example, portions of a wellhead assembly 10including a seal assembly 21, which may be a seal assembly according toany of the embodiment of the present application. The wellhead assembly10 can include an outer tubular 12 affixed at an upper end of a wellbore(not shown) and coaxially circumscribing an inner tubular 14. The outertubular 12 may be, for example, a high-pressure wellhead housing or acasing hanger. The inner tubular 14 may be, for example, a casinghanger, casing, tubing hanger, production tubing, or an isolationsleeve.

Inner tubular 14 transitions from an upper region with a larger outerdiameter 26 higher within the wellhead assembly 10, to a lower regionwith a smaller outer diameter 28 lower within the wellhead assembly 10through a downward facing shoulder 30. Outer tubular transitions from anupper region with a larger inner diameter 32 higher within the wellheadassembly to a lower region with a smaller inner diameter 34 lower withinthe wellhead assembly 10 through an upward facing shoulder 36.

The spaced apart distance between the respective inner surface 16 ofouter tubular 12 and outer diameter surface 18 of the inner tubular 14,respectively form an annulus 20. Within annulus 20 is seal assembly 21.Seal assembly 21 is ring shaped. The diameter of the opening in thecenter of the ring shaped assembly 21 is sized so that inner diametersealing surface 22 of seal assembly 21 makes contact with the outerdiameter surface 18 of the inner tubular 14. The outer diameter of thering shaped assembly 21 is sized so that outer diameter sealing surface24 of seal assembly 21 makes contact with inner surface 16 of outertubular 12. Embodiments of seal assembly 21 are shown in FIGS. 2-6.

Turning now to FIG. 2, in one embodiment, the seal assembly may comprisean energizer 38. Energizer 38 is shown as a single “U” section shapedring creating an upward facing internal slot or groove 39. Internalgroove 39 results in energizer 38 having an outer leg 41 and an innerleg 43, defined by the shape of internal groove 39. Energizer 38comprises an outer circumferential recess 40 on the outer surface 42 ofenergizer 38 and an inner circumferential recess 44 on the inner surface46 of energizer 38. Outer circumferential recess 40 contains an outerdiameter sealing ring 48 and inner circumferential recess 44 contains aninner diameter sealing ring 50. Sealing rings 48, 50 are shown with asolid square cross section but they may have other alternative crosssections, such as rectangular, semi-circular, circular, oval, or otherworkable shape. Sealing rings 48, 50 may be extruded, machined complete,compression formed from wire and joined at the ends or fabricated byother known methods.

As is shown in FIG. 2, when energizer 38 is not positioned withinannulus 20 (FIG. 3), the axial height of outer circumferential recess 40is bigger than the axial height of outer diameter sealing ring 48 andthe axial height of inner circumferential recess 44 is bigger than theaxial height of inner diameter sealing ring 50. This allows room forsealing rings 48, 50 to expand in height when the width of the sealingrings 48, 50 is compressed, as shown in FIG. 3, when seal assembly 21 islocated within annulus 20. Sealing rings 48, 50 are not fixed or bondedto energizer 38. This avoids a complicated or costly bonding process,allows for easy replacement of the sealing rings 48,50, and allows thesealing rings 48, 50 to more readily flow into defects.

Energizer 38 has circumferential bands or protrusions 52 that projectoutward from outer surface 42 of energizer 38 above and below outercircumferential recess 40. Circumferential bands or protrusions 54project inward from inner surface 46 of energizer 38 above and belowinner circumferential recess 44. Protrusions 52, 54 have circumferentialend surfaces 56, 58, respectively. Annular recesses 40, 44 are locatedwith in each of the bands 52, 54 respectively.

As show in FIG. 3, when energizer 38, is located within annulus 20,outer sealing ring 48 is in sealing engagement with inner surface 16 ofouter tubular 12 and the energizer 38. Inner sealing ring 50 is insealing engagement with outer diameter surface 18 of the inner tubular14 and energizer 38. Energizer 38 is positioned above downward facingshoulder 30 of inner tubular 14 and below upward facing shoulder 36 ofouter tubular 12. In alternative embodiments, shoulder 30 may be upwardfacing and shoulder 36 may be downward facing. In yet other alternativeembodiments, shoulders 30, 36 may both face upwards or both facedownwards. Internal groove 39 of energizer 38 is open to the pressure ofthe well fluid contained within annulus 20. In the embodiment of FIG. 3,the pressure side is at the higher end of annulus 20 and thereforeinternal groove 39 opens upward. In alternative embodiment, the pressureside may be at the lower end of annulus 20, in which case, the groove 39would open downward. A retainer ring 60 is located below energizer 38 tolimit downward movement of energizer 38 within annulus 20.

Seal assembly 21 may be installed within annulus 20 with a interferencebetween the inner surface 16 of outer tubular 12 and outer diametersurface 18 of the inner tubular 14. In this case, the initial radialdimension of the energizer 38, measured from end surface 56 to endsurface 58 is larger than the distance between inner surface 16 of outertubular 12 and the energizer 38, outer diameter surface 18 of the innertubular 14. Similarly, the initial radial dimension from inner surface55 of the inner diameter seal ring 50 to an outer surface 57 of theouter diameter seal ring 48 greater than a radial width of the annulusbetween inner surface 16 of outer tubular 12 and the energizer 38, outerdiameter surface 18 of the inner tubular 14. Therefore legs 41, 43 ofenergizer 38 will have to deflect inward towards each other wheninserted within annulus 20. This inward deflection of legs 41, 43 ofenergizer 38 generate an outward radial elastic load. This will causesealing rings 48, 50 to be compressed between inner surface 16 of outertubular 12 and the energizer 38, outer diameter surface 18 of the innertubular 14 and energizer 38, respectively.

The compressive forces causes plastic or permanent deformation ofsealing rings 48, 50, causing them to fill the recesses 40 and 44 and toseal with and fill any defects in outer tubular 12 and inner tubular 14.The deformation of sealing rings 48, 50 is contained to the interior ofrecesses 40, 44, which act as anti-extrusion means. End surfaces 56, 58of protrusions 52 and 54 will contact the inner surface 16 of outertubular 12 and outer diameter surface 18 of the inner tubular 14,respectively, to limit the outward radial forces on sealing rings 48,50. The combination of the elastic deformation of energizer 38 andplastic deformation of sealing rings 48, 50 creates a constant elasticcontact pressure at each of the sealing interfaces which does notdiminish with time or load history or temperature, and creates a seal atlow pressure and also possibly at high pressure.

Alternatively, the radial outward elastic load of energizer 38 may becreated by the fluid pressure within annulus 20. In this embodiment, thefluid pressure within annulus 20 and groove 39 will act on the insidesurfaces of groove 39, which is open to the pressure of the fluidcontained within annulus 20, applying a radial force on legs 41, 43. Inthe same manner as discussed above, this will cause sealing rings 48, 50to be compressed between inner surface 16 of outer tubular 12 and theenergizer 38, and the outer diameter surface 18 of the inner tubular 14and energizer 38, respectively.

The compression causes plastic or permanent deformation of sealing rings48, 50, causing them to fill the recesses 40 and 44. The deformation ofsealing rings 48, 50 is contained to the interior of recesses 40, 44,which act as anti-extrusion means. End surfaces 56, 58 of protrusions 52and 54 will contact the inner surface 16 of outer tubular 12 and outerdiameter surface 18 of the inner tubular 14, respectively, to limit theoutward radial forces on sealing rings 48, 50. The combination of theelastic deformation of energizer 38 and plastic deformation of sealingrings 48, 50 creates a constant elastic contact pressure at each of thesealing interfaces. In this case, a drop in pressure may cause a drop inelastic loading of the energizer 38. Another alternative embodiment isto combine both an interference fit and fluid pressure loading onenergizer 38. In this embodiment, the energizer 38 and seal rings 48, 50will still maintain a seal in the event of a complete loss of fluidpressure, but the elastic forces of energizer 38 may be augmented byfluid pressure within annulus 20 and groove 39.

Sealing rings 48, 50 are formed of soft inelastic materials and may befor example, a soft metal such as lead, tin, silver, gold or tantalum,an inelastic thermoplastic, such as virgin polytetrafluoroethylene,filled polytetrafluoroethylene or polyetheretherketone, or other inertinelastic materials such as compression molded graphite. Sealing rings48, 50 may alternatively be formed of other soft inelastic materials. Anappropriate soft inelastic material will be selected so that sealingrings 48, 50 will flow readily into defects on the inner surface 16 ofouter tubular 12 and the outer diameter surface 18 of the inner tubular14 and create sufficient contact pressure on the surface of any suchdefect to create a seal when subjected to radial loading. Where there isno defect present the sealing rings 48, 50 will simply deform and flowupwards and downwards in the recesses 40, 44 to fill the availablespace, while creating a seal on the defect free inner surface 16 ofouter tubular 12 and the outer diameter surface 18 of the inner tubular14.

Energizer 38 is formed from material that is strong enough to withstandthe internal fluid pressure within the annulus 20 as well as anyinternal loads generated by the interference fit between the energizer38, the inner surface 16 of outer tubular 12 and outer diameter surface18 of the inner tubular 14, without undergoing significant plasticdeformation, which could limit the load that could be applied toenergizer 38 or cause failure of energizer 38 and thus cause the sealassembly 21 to fail. Energizer 38 must therefore be made from materialwith higher strength or that is harder than the material used to makethe sealing rings 48, 50. Preferably, energizer 38 is made from steel,or where corrosion is of concern from steel or nickel based alloy.

In an alternative embodiment, as shown in FIG. 4, the seal assembly maycomprise two energizers, including a primary energizer 62 and a backsideenergizer 64. Energizers 62, 64 are shown as single “U” section shapedrings. Primary energizer 62 has an upward facing internal slot or groove66, which results in energizer 62 having an outer leg 68 and an innerleg 70, defined by the shape of internal groove 66. Backside energizer64 has a downward facing internal slot or groove 72, which results inenergizer 64 having an outer leg 74 and an inner leg 76, defined by theshape of internal groove 72. Energizers 62, 64 may have alternativeshaped cross sections.

Primary inner diameter seal ring 78 is located external to leg 70 ofprimary energizer 62 and primary outer diameter seal ring 80 is locatedexternal to leg 68 of primary energizer 62. Backside inner diameter sealring 82 is located external to leg 76 of backside energizer 64 andbackside outer diameter seal ring 84 is located external to leg 74 ofbackside energizer 64. Sealing rings 78, 80, 82, 84 are shown with asolid rectangular cross section but they may have other alternativecross sections, such as square, semi-circular, circular, oval, or otherworkable shape. Sealing rings 78, 80, 82, 84 may be extruded, machinedcomplete, compression formed from wire and joined at the ends orfabricated by other known methods.

An inner intermediate anti-extrusion ring 86 is located below primaryinner diameter seal ring 78 and above backside inner diameter seal ring82. A lateral portion 102 of inner intermediate anti-extrusion ring 86extends between primary energizer 62 and backside energizer 64. An outerintermediate anti-extrusion ring 88 is located below primary outerdiameter seal ring 80 and above backside outer diameter seal ring 84. Alateral portion 104 of outer intermediate anti-extrusion ring 88 extendsbetween primary energizer 62 and backside energizer 64.

In the embodiment of FIG. 4, intermediate anti-extrusion rings 86, 88are generally wedge shaped with upward facing shoulders 83 which engagedownward facing wedge surfaces or shoulders 85 of primary energizer 62.Downward facing wedge surface or shoulder 87 of anti-extrusion rings 86,88 engage upward facing shoulders 89 of backside energizer 64.

Primary anti-extrusion rings 90, 91 are located above primary seal rings78, 80 and backside anti-extrusion rings 92, 93 are located belowbackside seal rings 82, 84. In the embodiment of FIG. 4, the primaryanti-extrusion rings 90, 91 consist of a pair of rings with a wedgeshaped cross section. Outer primary anti-extrusion ring 90 has an uppersurface which is essentially horizontal and an angled downward facingsurface 94. Inner primary anti-extrusion ring 91 has a lower surfacewhich is essentially horizontal and an angled upward facing surface 96.Downward facing surface 94 of outer primary anti-extrusion ring 90engages upward facing surface 96 of Inner primary anti-extrusion ring91. Inner backside anti-extrusion ring 92 has an upper surface which isessentially horizontal and an angled downward facing surface 98. Outerprimary anti-extrusion ring 93 has a lower surface which is essentiallyhorizontal and an angled upward facing surface 100. Downward facingsurface 98 of inner backside anti-extrusion ring 92 engages upwardfacing surface 100 of outer backside anti-extrusion ring 93.

Before being inserted in an annulus, the inner diameter of the innerdiameter seal rings 78, 82 is smaller than the inner diameter of theprimary anti-extrusion rings 90, 91 intermediate inner anti-extrusionring 86, and backside anti-extrusion rings 92, 93. Similarly, the outerdiameter of the outer diameter seal rings 80, 84 is larger than theouter diameter of primary anti-extrusion rings 90, 91 intermediate outeranti-extrusion ring 88, and backside anti-extrusion rings 92, 93. Inaddition, the height of the seal rings 78, 80 is shorter than thedistance between the primary anti-extrusion rings 90, 91 and theintermediate anti-extrusion rings 86, 88. The height of the seal rings82,84 is shorter than the distance between the intermediateanti-extrusion rings 86, 88, and the backside anti-extrusion rings 92,93. This allows room for sealing rings 78, 80, 82, 84 to expand inheight when the width of the sealing rings 78, 80, 82, 84 is compressed,as shown in FIG. 5, when seal assembly 21 is located within annulus 20.Sealing rings 78, 80, 82, 84 are not fixed or bonded to energizers 62,64. This avoids a complicated or costly bonding process, allows for easyreplacement of the sealing rings 78, 80, 82, 84, and allows the sealingrings 78, 80, 82, 84 to more readily flow into defects.

When seal assembly 21 of FIG. 5 is positioned within an annulus 20,primary outer diameter seal ring 80, is in sealing engagement with innersurface 16 of outer tubular 12 and with the primary energizer 62.Primary inner diameter seal ring 78 is in sealing engagement with outerdiameter surface 18 of the inner tubular 14 and with primary energizer62. Backside outer diameter seal ring 84, is in sealing engagement withinner surface 16 of outer tubular 12 and with the backside energizer 64.Backside inner diameter seal ring 82 is in sealing engagement with outerdiameter surface 18 of the inner tubular 14 and with backside energizer64. Seal assembly 21 is positioned above downward facing shoulder 30 ofinner tubular 14 and below upward facing shoulder 36 of outer tubular12.

As shown in FIG. 6, when seal assembly 21 is fully set within annulus20, backside anti-extrusion rings 92, 93 will be restrained from furtherdownward movement. For example, backside anti-extrusion rings 92, 93 mayland on shoulders 106 on the inner surface 16 of outer tubular 12 andouter diameter surface 18 of the inner tubular 14. In alternativeembodiments, a retainer ring or similar devise may be used instead.

By continuing to apply a downwards force to primary anti-extrusion rings90, 91, downward facing surface 98 of inner backside anti-extrusion ring92 engages and slides along upward facing surface 100 of outer backsideanti-extrusion ring 93. This causes the inner backside anti-extrusionring 92 to move towards and come into contact with inner surface 16 ofouter tubular 12 and outer backside anti-extrusion ring 93 to movetowards and come into contact with outer diameter surface 18 of theinner tubular 14. Backside anti-extrusion rings 92, 93 will togetherthen cover the full diameter of annulus 20, limiting the downwardexpansion of backside seal rings 82, 84.

This downward force on primary anti-extrusion rings 90, 91 will causeprimary energizer 62 to move towards backside energizer 64. This causesupward facing shoulders 83 of intermediate anti-extrusion ring to engagedownward facing shoulders 85 of primary energizer 62, and downwardfacing shoulder 87 of anti-extrusion rings 86, 88 engage upward facingshoulders 89 of backside energizer 64, forcing the intermediate outeranti-extrusion ring 88 to move towards inner surface 16 of outer tubular12 and intermediate inner anti-extrusion ring 86 to move towards outerdiameter surface 18 of the inner tubular 14. Movement of theanti-extrusion rings 86, 88 may be limited either by inner surface 16 ofouter tubular 12 and outer diameter surface 18 of the inner tubular 14respectively, or by the closed ends of energizers 62, 64 contactingupper and lower surfaces of lateral portions 102, 104 of anti-extrusionrings 86, 88.

The downward force on primary anti-extrusion rings 90, 91 willadditionally cause downward facing surface 94 of outside primaryanti-extrusion ring 90 engages and slide along upward facing surface 96of inner primary anti-extrusion ring 91. This will result in innerprimary anti-extrusion ring 90 to moving towards and coming into contactwith outer diameter surface 18 of the inner tubular 14 and outer primaryanti-extrusion ring 91 moving towards and coming into contact with innersurface 16 of outer tubular 12. Primary anti-extrusion rings 90, 91 willtogether then cover the full diameter of annulus 20, limiting the upwardexpansion of primary seal rings 78, 80. A retaining mechanism, such asretaining ring 108 will be used to maintain the downward force onprimary anti-extrusion rings.

Seal assembly 21 may be installed within annulus 20 with a interferencebetween the inner surface 16 of outer tubular 12 and outer diametersurface 18 of the inner tubular 14. The compression on the energizers62, 64 causes legs 68, 70 of primary energizer 62 and legs 74, 76 ofbackside energizer 64 to deflect inwardly, generating an outward radialelastic load. This will cause sealing rings 80, 84 to be compressedbetween inner surface 16 of outer tubular 12 and the energizers 62, 64respectively, and sealing rings 78, 82 to be compressed between outerdiameter surface 18 of the inner tubular 14 and energizers 62, 64,respectively. The compressive forces causes plastic deformation ofsealing rings 78, 80, 82, 84, causing them to deform and become thinnerand taller. The increase in height of sealing rings 78, 80 is containedto the space between the primary anti-extrusion rings 90, 91 and theintermediate anti-extrusion rings 86, 88. The increase in height ofsealing rings 82, 84 is contained to the space between the intermediateanti-extrusion rings 86,88 and the backside anti-extrusion rings 92, 93.The combination of the elastic deformation of energizers 62, 64 andplastic deformation of sealing rings 78, 80, 82, 84 creates a constantelastic contact pressure at each of the sealing interfaces which doesnot diminish with time or load history or temperature, and creates aseal at low pressure and also possibly at high pressure.

Alternatively, the radial outward elastic load of energizers 62, 64 maybe created by the fluid pressure within grooves 66, 72, which applies anoutward force on legs 68, 70, 74, 76, casing outward radial deflectionsof legs 68, 70, 74, 76. In the same manner as discussed above, this willcause sealing rings 78, 80, 82, 84 to be compressed between innersurface 16 of outer tubular 12 and the energizers 62, 64, and the outerdiameter surface 18 of the inner tubular 14 and energizers 62, 64,respectively. The compressive forces causes plastic deformation ofsealing rings 78, 80, 82, 84, causing them to deform and become thinnerand taller. The increase in height of sealing rings 78, 80 is containedto the space between the primary anti-extrusion rings 90, 91 and theintermediate anti-extrusion rings 86, 88. The increase in height ofsealing rings 82, 84 is contained to the space between the intermediateanti-extrusion rings 86,88 and the backside anti-extrusion rings 92, 93.The combination of the elastic deformation of energizers 62, 64 andplastic deformation of sealing rings 78, 80, 82, 84 creates a constantelastic contact pressure at each of the sealing interfaces.

Sealing rings 78, 80, 82, 84 are formed of soft inelastic materials andmay be for example, a soft metal such as lead, tin, silver, gold ortantalum, an inelastic thermoplastic, such as virginpolytetrafluoroethylene, filled polytetrafluoroethylene orpolyetheretherketone, or other inert inelastic materials such ascompression molded graphite. Sealing rings 78, 80, 82, 84 mayalternatively be formed of other soft inelastic materials. Anappropriate soft inelastic material will be selected so that sealingrings 78,80, 82, 84 will flow readily into defects on the inner surface16 of outer tubular 12 and the outer diameter surface 18 of the innertubular 14 and create sufficient contact pressure on the surface of anysuch defect to create a seal when subjected to radial loading. Wherethere is no defect present the sealing rings 78, 80, 82, 84 will simplydeform and flow upwards and downwards to fill the available space, whilecreating a seal on the defect free inner surface 16 of outer tubular 12and the outer diameter surface 18 of the inner tubular 14.

Energizers 62, 64 are formed from material, such as steel or nickel oralloy thereof, that is strong enough to withstand the internal fluidpressure within the annulus 20 as well as any internal loads generatedby the interference fit between the energizers 62, 64, the inner surface16 of outer tubular 12 and outer diameter surface 18 of the innertubular 14, without undergoing significant plastic deformation, whichcould limit the load that could be applied to energizers 62, 64 or causefailure of energizer 62, 64 and thus cause the seal assembly 21 to fail.Energizers 62, 64 must therefore be made from material with higherstrength or that is harder than the material used to make the sealingrings 78, 80, 82, 84.

In the drawings and specification, there have been disclosed a typicalpreferred embodiment of the invention, and although specific terms areemployed, the terms are used in a descriptive sense only and not forpurposes of limitation. The invention has been described in considerabledetail with specific reference to these illustrated embodiments. It willbe apparent, however, that various modifications and changes can be madewithin the spirit and scope of the invention as described in theforegoing specification. For example, although primarily illustrated inthe context of a casing hanger landed within a modified high-pressurewellhead housing, one of ordinary skill in the art will recognize thatthe featured seal assembly and methods can be readily employed withrespect to tubing within modified casing or other tubing.

1. A seal assembly for sealing an annulus between inner and outerwellhead members, the seal assembly comprising: an energizer ring havinginner and outer legs separated by a slot, formed of a high strengthelastic material and having a central axis; an inner diameter seal ringformed of an inelastic material located on an inner side of the innerleg for creating a seal between the inner wellhead member and theenergizer; and an outer diameter seal ring formed of an inelasticmaterial located on an outer side of the outer leg for creating a sealbetween the energizer and the outer wellhead member.
 2. The sealassembly of claim 1, wherein the seal assembly has an initial radialdimension from inner surface of the inner diameter seal ring to an outersurface of the outer diameter seal ring that is adapted to be greaterthan a radial width of the annulus, causing the legs of the energizer todeflect towards each other when inserted in the annulus.
 3. The sealassembly of claim 1 further comprising a plurality of anti-extrusiondevices for restricting an axial dimension of each of the seal ringswhen the seal assembly is set.
 4. The seal assembly of claim 3, whereinthe anti-extrusion devices comprises: an annular band on the inner sideof the inner leg and protruding inward from the inner leg; an annularband on the outer side of the outer leg and protruding outward from theouter leg; an annular recess in each of the bands; and wherein each ofthe seal rings is located in one of the recesses and radially protrudestherefrom prior to setting of the seal assembly.
 5. The seal assembly ofclaim 4, wherein prior to setting of the seal assembly, an axialdimension of each annular recess is greater than an axial dimension ofeach seal ring.
 6. The seal assembly of claim 4, wherein the annularbands are adapted to contact the inner and outer wellhead members whenthe seal ring assembly is set.
 7. The seal assembly of claim 3, whereinthe anti-extrusion devices comprise a pair of wedge rings, the wedgerings having a mating wedge surface that causes one of the wedge ringsto slide radially inward and the other to slide radially outward.
 8. Theseal assembly of claim 3, wherein the anti-extrusion device comprises:an inner wedge ring having an inner wedge ring surface; an outer wedgering having an outer wedge ring surface; and inner and outer wedgesurfaces on a base of the energizer that slidingly engage the innerwedge ring surface and the outer wedge ring surface during setting ofthe seal assembly to convey the wedge rings apart from each other. 9.The seal assembly of claim 1, further comprising: a second energizerring having inner and outer legs facing in an opposite direction to saidfirst mentioned energizer ring.
 10. The seal assembly of claim 1,wherein the inner diameter seal ring and the outer diameter seal ringare formed of an inelastic material selected from a group consisting oflead, tin, silver, gold, tantalum, virgin polytetrafluoroethylene,filled polytetrafluoroethylene, polyetheretherketone, or compressionmolded graphite.
 11. A wellhead assembly comprising: an outer wellheadmember having a bore and an axis; an inner wellhead member located inthe bore and defining an annulus between the inner and outer wellheadmembers; an energizer ring having inner and outer legs separated by aslot, formed of an elastic material and having a central axis; an innerdiameter seal ring formed of an inelastic material located on an innerside of the inner leg for creating a seal between the inner wellheadmember and the energizer; an outer diameter seal ring formed of aninelastic material located on an outer side of the outer leg forcreating a seal between the energizer and the outer wellhead member;wherein the legs deflect towards each other when inserted in theannulus, causing the seal rings to radially deform.
 12. The wellheadassembly of claim 11 further comprising a plurality of anti-extrusiondevices for restricting an axial dimension of each of the seal ringswhen set in the annulus.
 13. The wellhead assembly of claim 12, whereinthe anti-extrusion devices comprise: an annular band on the inner sideof the inner leg and protruding inward from the inner leg; an annularband on the outer side of the outer leg and protruding outward from theouter leg; an annular recess in each of the bands; and wherein prior tosetting of the seal assembly, each of the seal rings is located in oneof the recesses and radially protrudes therefrom, and an axial dimensionof each annular recess is greater than an axial dimension of each sealring.
 14. An apparatus for sealing an annulus between inner and outerwellhead members, the seal assembly comprising: a first energizer ringhaving inner and outer legs separated by a slot, formed of a highstrength elastic material and having a central axis; a second energizerring having inner and outer legs facing in an opposite direction to thefirst energizer ring; an inner diameter seal ring formed of an inelasticmaterial located on an inner side of each of the inner legs for creatinga seal between the inner wellhead member and the energizers; an outerdiameter seal ring formed of an inelastic material located on an outerside of each of the outer legs for creating a seal between theenergizers and the outer wellhead member; and a plurality ofanti-extrusion devices for restricting an axial dimension of each of theseal rings when the seal assembly is set.
 15. The apparatus of claim 14,wherein when a force is applied in an axial direction to set theapparatus in the annulus, the inner seal rings move inward to abut theinner wellhead member and the outer seal rings move outward to abut theouter wellhead member.
 16. The apparatus of claim 15, wherein the antiextrusion devices comprise: an inner wedge ring having an inner wedgering surface; an outer wedge ring having an outer wedge ring surface;inner and outer wedge surfaces on a base of each energizer thatslidingly engage the inner wedge ring surface and the outer wedge ringsurface during setting of the apparatus to convey the wedge rings apartfrom each other.
 17. A method for sealing an annulus between inner andouter wellhead members, the method comprising the steps of: (a)positioning an energizer within the annulus, the energizer ring havinginner and outer legs separated by a slot, formed of an elastic materialand having a central axis; (b) creating a seal between the innerwellhead member and the energizer with an inner diameter seal ringformed of an inelastic material located on an inner side of the innerleg; and (c) creating a seal between the energizer and the outerwellhead member with an outer diameter seal ring formed of an inelasticmaterial located on an outer side of the outer leg.
 18. The method ofclaim 17, wherein steps (b) and (c) further comprise applying sufficientforce to the energizer to deflect the legs of the energizer towards eachother by elastic deformation and cause plastic deformation of the innerdiameter seal ring and outer diameter seal ring.
 19. The method of claim17, wherein steps (b) and (c) further comprise providing a fluid underpressure within the slot to apply a radial force on the legs and causeplastic deformation of the inner diameter seal ring and outer diameterseal ring.
 20. The method of claim 17 further comprising the step oflimiting the axial expansion of the inner diameter seal ring and theouter diameter seal ring with an anti-extrusion device.
 21. The methodof claim 20, wherein the step of limiting the axial expansion of theinner diameter seal ring and the outer diameter seal ring is performedby an annular band on the inner side of the inner leg and protrudinginward from the inner leg and an annular band on the outer side of theouter leg and protruding outward from the outer leg, wherein an annularrecess is formed in each of the bands and wherein prior to setting ofthe seal assembly: each of the seal rings is located in one of therecesses and radially protrudes therefrom; and an axial dimension ofeach annular recess is greater than an axial dimension of each sealring.